[MAP] Light recycling; Piccione lip

Valeri A Lebedev val at fnal.gov
Fri Dec 21 12:26:03 EST 2012


Hi to everybody,
It has been a lovely discussion. I just would like to note that it is already taken into account. Our muon production is based on the "light recycling". Strong magnetic field and thin target do the same thing. For sufficiently thin target and large magnetic field the phase density of pions is proportional to the magnetic field!!! Is not it the same phenomenon.
I do not think there is another trick which we could apply to get even more but I would not exclude it. The nature does not squeeze us to Hamiltonian systems only.
Merry Christmas and Happy New Year.
Valeri

From: map-l-bounces at lists.bnl.gov [mailto:map-l-bounces at lists.bnl.gov] On Behalf Of Kirk T McDonald
Sent: Thursday, December 20, 2012 6:40 PM
To: Andrew Sessler; Kirk T McDonald
Cc: MAP-l at lists.bnl.gov
Subject: Re: [MAP] Light recycling; Piccione lip

Andy,

If the phosphor simply absorbed the photons that hit it, and did not re-emit them, the brightness of the hole would be the same as the brightness of the phosphor surface - even though the emittance of the hole is much smaller than the total emittance of the phosphor surface.

[This is the usual version of the brightness theorem.]

---------------------------------------------
What is special about the aperture lamp is the the photons that do not immediately go out the hole are not wasted, but eventually get out - and into the same transverse phase space as the photons that got out on the first try.

In this case, more photons/sec emerge from the hole than we expected from a more ordinary lamp.

And, the brightness is thereby increased.

------------------------------
When multiple bunches are injected into a storage ring, we don't succeed in putting them into the same region of phase space.  Rather, they are put into adjacent regions (phase-space painting).   This increases the number of particles in the circulating bunch, but the brightness of that bunch is not increased.

Whereas, the the aperture lamp, a photon goes into the same region of phase space not matter how many tries it takes to get there.

--Kirk

PS  Your comments have sharpened my thinking about this interesting process.   As a result, I've updated my note, with new footnotes 6, 9 and 25.
http://puhep1.princeton.edu/~mcdonald/examples/lamp.pdf

Thanks for prompting me in this way.




From: Andrew Sessler<mailto:amsessler at lbl.gov>
Sent: Thursday, December 20, 2012 12:51 PM
To: Kirk T McDonald<mailto:kirkmcd at Princeton.EDU>
Cc: MAP-l at lists.bnl.gov<mailto:MAP-l at lists.bnl.gov>
Subject: Re: [MAP] Light recycling; Piccione lip

Thursday
Dear Kirk,
I think I would say it differently and I would appreciate your comment: "Wrong!, Okay, Partially."
The photon number doesn't increase at each reflection, so the only effect is that the photon is bounced back and forth until it hits the hole and gets out. So, the effect is simply reducing the emittance from 4 pi (the whole sphere) to the area of the hole. Even simple to calculate the amplification. So, my view is not a re-using of photons, but a change in desired emittance.
Andy

On Wed, Dec 19, 2012 at 8:36 PM, Kirk T McDonald <kirkmcd at princeton.edu<mailto:kirkmcd at princeton.edu>> wrote:
Folks,

I have become fortuitously aware of an old trick in the lamp industry that is now sometimes called "light recycling" - with the goal of enhancing the optical brightness of light sources.

Remember, brightness = power / area in transverse phase space
(although the opticians don't generally say it this way, perhaps using the buzzword "etendue" instead of "area in transverse phase space")
In our project, we try to increase the brightness by "cooling"/shrinking the area in transverse phase space.

The opticians' trick is to "recycle" the light so that one photon gets counted many times in the same area in phase space, effectively increasing the power, while leave the emittance the same.

The historical way of doing this (dating back at least to 1936) involves a cylindrical cavity lined with a phosphor (i.e., a fluorescent lamp) with a small slit in the phosphor to let light out.

A photon has only a small probability P to escape out the slit directly after being emitted by the phosphor.

Generally, the photon hits another region of the phosphor, is absorbed, and then re-emitted.  [The cavity can be lined with a reflector to assist in this process.]

On average, the photon bounces around N = 1 / P times before it escapes through the slit.

Hence, the steady-state emission of photons by the phosphor surface is N times greater than if the photons flew away on their first emission - as holds for an ordinary fluorescent lamp.

The net effect is that the light coming out of the slit is N times brighter than the light from an ordinary fluorescent bulb of the same output power.

The brightness has been enhanced N-fold (with no emittance reduction) to the extent that the absorption and re-emission involves no losses.

[I think the lamps in Xerox machines and scanners are of this type.]

I've written up a pedagogic note on this:
http://puhep1.princeton.edu/~mcdonald/examples/lamp.pdf

--------------------------------------
This trick seems different from what we do to enhance the brightness of particle beams.

However, a comment by Fred Mills, dated 9/98, near the bottom of my web page
http://puhep1.princeton.edu/~mcdonald/mumu/physics/
has me wondering if part of the effect of the "Piccione lip" seen on p. 4 of
http://puhep1.princeton.edu/~mcdonald/mumu/physics/lichtenberg_mura-110.pdf
was to use multiple scattering in the "lip" to kick some particles into a desired area of phase space.

That is, perhaps we can say that ionization cooling also includes a small effect equivalent to the opticians' trick of "light recycling".

What do you think?

--Kirk

PS  The opticians are after big game = use of such tricks to make better solar energy concentrators for photovoltaic energy generation (or even just heating water).

In the past, such efforts have not involved brightness enhancement, but only clever rearrangement of light in phase space (as in Winston cones).

The next generation of brightness enhancement schemes uses materials with differing absorption and emission spectra to play additional "tricks".   New engineered optical materials, called photonic band gap materials, could play a key role here.

If these solar brightness-enhancement schemes pay off, they will be able to fund all of high energy physics....

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